Chronic hepatitis C is a disease characterized in that the infection of hepatitis C viruses (HCV) continuously induces inflammation in liver centering around the area of portal vein, and advances to hepatic cirrhosis or primary hepatocellular carcinoma. Contrary to hepatitis A or B, about 90% of hepatitis C shows abnormal GPT (glutamic-pyruvic transaminase) level, even at the primary infection, and develops into chronic illness. Recently, it is reported that hepatitis C virus may directly participate in the induction of hepatocellular carcinoma [see, Sakamuro, Furukawa and Takegami, J. Virol. 69: 3893-3896, 1995; Ray, Logging, Meyer and Ray, J. Virol. 70: 4438-4443, 1996]. In addition, it is also reported that hepatitis C virus is detected in 30% of patients with hepatocellular carcinoma in western countries [see, Mangia, Vallari and Bisceglie, J. Med. Virol. 43, 125-128, 1994].
According to the development of HCV antibody (C100-3 antibody) detection system by Chiron Inc. (U.S.A.) in 1988, it has been revealed that the majority of non-A, non-B hepatitis are caused by hepatitis C virus. In Japan, the screening assay using antibody detection system has allowed to demonstrate that hepatitis C virus is detected in 70% of patients suffering from non-A, non-B hepatitis and in 90% or more of hepatoma patients.
In 1989, the nature of hepatitis C virus was first identified by separating a part of virus gene from the serum of chimpanzee suffering from non-A, non-B hepatitis. That is, hepatitis C virus belongs to Flaviviridae having 9.5 kb positive(+)-stranded RNA as a gene, and synthesizes viral polypeptide precursor in host cells. The precursor protein is transformed into structural proteins (core, E1, E2), which are directly comprised to make up the viral structure, and non-structural proteins (NS2, NS3, NS4A, NS4B, NS5A, NS5B) having enzymatic activities after the post-translational modification by the signal peptidase of a host, and by metalloprotease and serine protease produced from hepatitis C virus. Particularly, numerous variants can be produced due to the presence of two hypervariable regions (HVR1 and HVR2) on the 5' end of E2 gene.
Although the mechanism related to the progression from chronic hepatitis C to hepatocellular carcinoma has not been yet established, chronic inflammation and the intensity of inflammation may be closely related. That is, although the host immune system produces neutralizing antibody against hepatitis C virus, the neutralizing antibody affects only the limited types of viruses, and the variants resistant to the neutralizing antibody are produced quickly (genetic mutation at high rate). In spite of the presence of the neutralizing antibody, the variants may continuously induce inflammation in the host (immune escape). Further, the regeneration ability of host liver cells from the continuous infectious damages may cause tumorigenesis. Recently, it has been reported that double strand RNA-dependent protein kinase R (PKR) of host cells can phosphorylate elF-2a to stimulate apoptosis of virus. However, hepatitis C virus produces proteins capable of inactivating PKR. For example, it may be explained that the resistance of hepatitis C virus to the administration of interferon is caused by inactivation of PKR by the variants of hepatitis C virus. Hence, the presence of variants is an obstacle to the production of vaccine against hepatitis C virus.
Due to such characteristics of hepatitis C virus, many drugs currently being, used as a therapeutic agent for the treatment of hepatitis C cannot provide a sufficient therapeutic effect. The effects of interferon may prevent the incidence of hepatic cirrhosis and hepatocellular carcinoma originated from hepatitis C, rather than actually reduce hepatitis C virus. Further, clinical studies report numerous adverse effects of interferon. Hence, there is a prevalent course for studies and researches in the scientific community to find and develop the inhibitors of hepatitis C virus protease for the treatment of hepatitis C.
The present inventors have extensively studied to find out the material which resolves the problems involved in the prior therapeutic agents used for treatment of hepatitis C such as interferon, and which has an immunopotentiating activity as well as an anti-viral activity against hepatitis C virus for an effective treatment. Particularly, the inventors have studied various natural medicinal plants as the subject their research. As a result, it has been concluded that among numerous natural plants the mixed extract obtained from the mixture of Phellodendron amurense RUPRECHT cortex and Patrinia scabiosaefolia FISCH. can accomplish the purpose of the present invention as mentioned above.